A long-term follow-up was planned and approved for five years with annual contact by mail and telephone of the cohort which includes 4,275 women with breast cancer; 25,066 women with benign breast disease; 25,163 women who are matched to the benign cases by age, date of entry, geographic location of the project, and race; and 9,681 women for whom a recommendation at screening was made for surgical consultation either aspiration or biopsy, but was not performed. Between January 1, 1980, and March 1, 1981, twenty-eight interview projects were established to submit required data to a central Data Management and Analysis Center, which is responsible for the collection, processing, managing, and analyzing the data generated by the centers. The contract establishes the Data Management and Analysis Center which is essential to conduct the long-term follow-up study.